/**
 * Provides a method to encode any string into a URL-safe form.<br>
 * Non-ASCII characters are first encoded as sequences of two or three bytes, using the UTF-8 algorithm, before being
 * encoded as %HH escapes.<br>
 * URLUTF8Encoder: http://www.w3.org/International/URLUTF8Encoder.java<br>
 * Copyright � 1997 World Wide Web Consortium, (Massachusetts Institute of Technology, European Research Consortium for
 * Informatics and Mathematics, Keio University). All Rights Reserved. This work is distributed under the W3C� Software
 * License [1] in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. [1]
 * http://www.w3.org/Consortium/Legal/2002/copyright-software-20021231<br>
 * Created: 17 April 1997
 * @author Bert Bos <bert@w3.org>
 */

package org.chipu.shared.util.singletons;

public class URLUTF8Encoder {
	final static String[] hex = {"%00", "%01", "%02", "%03", "%04", "%05", "%06", "%07", "%08", "%09", "%0a", "%0b", "%0c",
		"%0d", "%0e", "%0f", "%10", "%11", "%12", "%13", "%14", "%15", "%16", "%17", "%18", "%19", "%1a", "%1b", "%1c", "%1d",
		"%1e", "%1f", "%20", "%21", "%22", "%23", "%24", "%25", "%26", "%27", "%28", "%29", "%2a", "%2b", "%2c", "%2d", "%2e",
		"%2f", "%30", "%31", "%32", "%33", "%34", "%35", "%36", "%37", "%38", "%39", "%3a", "%3b", "%3c", "%3d", "%3e", "%3f",
		"%40", "%41", "%42", "%43", "%44", "%45", "%46", "%47", "%48", "%49", "%4a", "%4b", "%4c", "%4d", "%4e", "%4f", "%50",
		"%51", "%52", "%53", "%54", "%55", "%56", "%57", "%58", "%59", "%5a", "%5b", "%5c", "%5d", "%5e", "%5f", "%60", "%61",
		"%62", "%63", "%64", "%65", "%66", "%67", "%68", "%69", "%6a", "%6b", "%6c", "%6d", "%6e", "%6f", "%70", "%71", "%72",
		"%73", "%74", "%75", "%76", "%77", "%78", "%79", "%7a", "%7b", "%7c", "%7d", "%7e", "%7f", "%80", "%81", "%82", "%83",
		"%84", "%85", "%86", "%87", "%88", "%89", "%8a", "%8b", "%8c", "%8d", "%8e", "%8f", "%90", "%91", "%92", "%93", "%94",
		"%95", "%96", "%97", "%98", "%99", "%9a", "%9b", "%9c", "%9d", "%9e", "%9f", "%a0", "%a1", "%a2", "%a3", "%a4", "%a5",
		"%a6", "%a7", "%a8", "%a9", "%aa", "%ab", "%ac", "%ad", "%ae", "%af", "%b0", "%b1", "%b2", "%b3", "%b4", "%b5", "%b6",
		"%b7", "%b8", "%b9", "%ba", "%bb", "%bc", "%bd", "%be", "%bf", "%c0", "%c1", "%c2", "%c3", "%c4", "%c5", "%c6", "%c7",
		"%c8", "%c9", "%ca", "%cb", "%cc", "%cd", "%ce", "%cf", "%d0", "%d1", "%d2", "%d3", "%d4", "%d5", "%d6", "%d7", "%d8",
		"%d9", "%da", "%db", "%dc", "%dd", "%de", "%df", "%e0", "%e1", "%e2", "%e3", "%e4", "%e5", "%e6", "%e7", "%e8", "%e9",
		"%ea", "%eb", "%ec", "%ed", "%ee", "%ef", "%f0", "%f1", "%f2", "%f3", "%f4", "%f5", "%f6", "%f7", "%f8", "%f9", "%fa",
		"%fb", "%fc", "%fd", "%fe", "%ff"};

	/**
	 * Encode a string to the "x-www-form-urlencoded" form, enhanced with the UTF-8-in-URL proposal. This is what
	 * happens:
	 * <ul>
	 * <li>The ASCII characters 'a' through 'z', 'A' through 'Z', and '0' through '9' remain the same.
	 * <li>The unreserved characters - _ . ! ~ * ' ( ) remain the same.
	 * <li>The space character ' ' is converted into a plus sign '+'.
	 * <li>All other ASCII characters are converted into the 3-character string "%xy", where xy is the two-digit
	 * hexadecimal representation of the character code
	 * <li>All non-ASCII characters are encoded in two steps: first to a sequence of 2 or 3 bytes, using the UTF-8
	 * algorithm; secondly each of these bytes is encoded as "%xx".
	 * </ul>
	 * @param s The string to be encoded
	 * @return The encoded string
	 */
	public static String encode(String s) {
		StringBuilder sbuf = new StringBuilder();
		int len = s.length();
		for(int i = 0; i < len; i++) {
			int ch = s.charAt(i);
			if ('A' <= ch && ch <= 'Z')
				sbuf.append((char) ch);
			else if ('a' <= ch && ch <= 'z')
				sbuf.append((char) ch);
			else if ('0' <= ch && ch <= '9')
				sbuf.append((char) ch);
			else if (ch == ' ')
				sbuf.append('+');
			else if (ch == '-' || ch == '_' // unreserved
				|| ch == '.' || ch == '!' || ch == '~' || ch == '*' || ch == '\'' || ch == '(' || ch == ')')
				sbuf.append((char) ch);
			else if (ch <= 0x007f)
				sbuf.append(hex[ch]);
			else if (ch <= 0x07FF) { // non-ASCII <= 0x7FF
				sbuf.append(hex[0xc0 | (ch >> 6)]);
				sbuf.append(hex[0x80 | (ch & 0x3F)]);
			} else { // 0x7FF < ch <= 0xFFFF
				sbuf.append(hex[0xe0 | (ch >> 12)]);
				sbuf.append(hex[0x80 | ((ch >> 6) & 0x3F)]);
				sbuf.append(hex[0x80 | (ch & 0x3F)]);
			}
		}
		return sbuf.toString();
	}
}